Polymeric dyes for antireflective coatings

ABSTRACT

A composition and methods for the use and manufacture thereof are provided for a polymeric dye. The composition comprises one or more aminoaromatic chromophores in conjunction with polymers having an anhydride group or the reaction products thereof. The composition is particularly useful as an underlaying antireflective coating with microlithographic photoresists for the absorbtion of near or deep ultraviolet radiation.

The application is a division of application Ser. No. 08/168,885, filedDec. 16, 1993 pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to novel compositions comprising dyeswhich are chemically linked to polymeric imides. Such compositions areuseful as antireflective layers or coatings. Such compositions are alsoespecially useful in the fabrication of integrated circuit devices byphotolithographic techniques.

2. Description of Related Art

In the fabrication of integrated circuits, the exposure of a photoresistto light is an integral process step. The production of high densitycircuits having sub micron dimensions requires that such exposure beaccomplished within close processing tolerances. For example, it isimportant to control the linewidth of the imaged and developedphotoresist so that any deviation from the nominal design linewidth overnon-planar or reflective features is small, typically less than 10%.

The difficulty in controlling linewidth in high resolution photoresistpatterns over reflective topography is well documented. See, forexample, D. Widmann and H. Binder, IEEE Trans. Electron Devices, ED-22,467 (1975). When photoresist layers overlaying reflective substrates areexposed using monochromatic light sources, a constructive interferencepattern between the normally incident exposing light and light reflectedfrom the substrate is created in the resist. The resulting pattern ofoptical nodes and antinodes which is normal to the plane of thereflective interface, and repeats along the optical axis, is the causeof localized variations in the effective dose of exposing light. Thisphenomenon is known in the art as the interference or standing waveeffect. Other pattern distortions are caused by light reflectedangularly from topographical features and are discussed by M. Bolsen, G.Buhr, H. Merrem, and K. Van Werden, Solid State Tech., February 1986,83. These distortions are known in the art as reflective notching.

The quantification of the interference effect can be measured by usingthe swing ratio (SR), set forth by T. Brunner, SPIE, 1466, 297 (1991),

    SR-4(R.sub.1 R.sub.2).sup.1/2 e.sup.-αD

where R₁ is the reflectivity of the resist/air interface and R₂ is thereflectivity of the resist/substrate interface at the exposingwavelength, α is the resist absorbtion coefficient, and D is the resistthickness. A low swing ratio implies that localized variations in theeffective dose of exposing light are small, and thus the exposure doseis more uniform throughout the thickness of the film. One method toreduce the swing ratio is use of a photoresist or lithographic processwhich imparts a high numerical value in α or D, giving a high numericalvalue to the product of αD. Other methods for reducing the swing ratioare the use of coatings which reduce the contribution of R1 or R2, suchas through the use of antireflective layers.

The lithographic techniques for overcoming the problems of formingpatterns on reflective topography include dyes added to the photoresistsas described in U.S. Pat. No. 4,575,480 to Kotani, et al., U.S. Pat. No.4,828,960 to Hertog, U.S. Pat. No. 4,882,260 to Kohara, et al., and U.S.Pat. No. 5,043,243 to Yajima, et al., top surface imaging (TSI)processes, multilayer resists (MLR) with added dyes as described in U.S.Pat. No. 4,370,405 to O'Toole, et al., top antireflective layers (TARL),bottom antireflective layers (BARL) which may comprise inorganicmaterials or organic materials, and coatings comprising polyamic acidsor polybutene sulfone with added dyes.

When a dye is added to photoresist to form an optically sensitive filmhaving high optical density at the wavelength of the exposing radiation,several problems may be encountered. These include sublimation of thedyes during baking of the films, loss of resist sensitivity,difficulties during deep ultra violet hardening processes which arecommonly used with novolak comprising resists, thinning of the resistsin alkaline developers, and distortion of the resulting relief image.TSI processes require high optical density at the wavelength of theexposing radiation and similar processing difficulties are oftenencountered. Furthermore, TSI and MLR processes are costly and complex.

Tanaka, et al., have disclosed the use of a TARL as an optical elementoverlaying a photoresist layer, however, this approach is not effectivein reducing top notching effects from underlaying reflective topographyand also requires removal with halogenated solvents prior to thephotoresist development step. T. Tanaka, N. Hasegwa, H. Shiraishi, andS. Okazaki, J. Electrochem. Soc., 137, 3900 (1990).

Inorganic BARLs such as silicon require precise control of the filmthickness, which for a typical 300 Å thick film is ±10 Å. T. Pampalone,M. Camacho, B. Lee, and E. Douglas, J. Electrochem. Soc., 136, 1181(1989). Pampalone has described the use of titanium oxynitrides onaluminum surfaces to reduce reflectivity from 85% to 25%, however,TiNxOy processes require special deposition--equipment, complex adhesionpromotion techniques prior to resist application, a separate dry etchingpattern transfer step, and dry etching for removal. Horn has disclosedthe similar use of titanium nitride antireflective coatings, however,.such coatings are often incorporated into the completed semiconductordevice as a permanent element, thus TiN coatings are not suitable foruse with every photolithographic layer. M. Horn, Solid State Tech.,November 1991, 58.

U.S. Pat. No. 4,910,122 to Arnold, et al., discloses organic BARLscomprising polyamic acids or polybutene sulfones with added dyes. Thefilms derived from the polyamic acid compositions are cured by baking ata temperature of at least 148° C. for 30 minutes. Pampalone has notedthat the baking conditions must be carefully controlled to prevent theoccurrence of oversized or undersized relief images in the imaged anddeveloped photoresist. Horn has noted that the BARL tended to peel orleave a residual scum. The polyamic acid based BARL is also developedwith alkaline developer of the resist. Concurrently, any Al layers whichmay be in contact with the BARL are attacked by the alkaline developer,which may cause lifting of the BARL and resist layer.

The films derived from polybutene sulfone with coumarin dyes requirecoating thicknesses of 2.0 μm and baking at 140° C. for 60 minutes. The2.0 μm thick film of polybutene sulfone may tend to fill in andplanarize deep trenches, resulting in localized regions having a filmthicker than 2.0 μm, and requiring plasma over etching to remove thefilm. The use of a 2.0 μm layer with an added 1.0 μm resist layer mayexceed the usual depth of focus of less than 2 μm for advanced, highernumerical aperture exposure tools. In addition long bake times are notcompatible with a rapid throughput cluster tool processing strategy,thus, such materials may require additional or separate long coating orbaking steps that add process costs. Polybutene sulfone is alsothermally unstable at temperatures above about 120° C. and may decomposewith out gassing. This may lift the overlying resist during deep ultraviolet hardening or Al etching where the wafer temperature may reach150° C.

U.S. Pat. No. 2,751,373 to Unruh, et al., U.S. Pat. No. 2,811,509 toSmith, et al., U.S. Pat. No. 3,763,086 to Kalopissis, et al., U.S. Pat.No. 3,854,946 to Sayigh, et al., and U.S. Pat. No. 4,609,614 toPampalone, et al., disclose the grafting of dyes or small molecules ontopolymeric structures consisting of poly(maleic anhydrides),poly(itaconic anhydrides), polyacrylates, and polymethacrylates. Theresulting polymers are ring opened products comprising a semi-amide inconjunction with a semi-acid or semi-ester. Most of the resultingpolymers are rapidly soluble in aqueous alkaline developers due to thepresence of acid or amide groups, and all have at least some appreciabledegree of solubility. Thus, these compositions would not be suitable asBARL materials for common resists using aqueous alkaline developers.Furthermore, all of the known compositions are soluble in solvents suchas those typically used to cast photoresist films. Therefore,intermixing of polymer layers during application of a BARL materialbased on these compositions would be a substantial disadvantage.

Czech patent 200,359 to Matejka similarly discloses compositionscomprising semi-amides derived from maleic anhydride copolymers, whichcompositions are also soluble in aqueous alkaline solutions.

BRIEF SUMMARY OF THE INVENTION

The present invention provides novel compositions which comprise thereaction product of a polymer having an anhydride group and an amine dyewhich strongly absorbs ultraviolet light having a wavelength in therange from about 365 nm to about 436 nm, or from about 193 nm to about300 nm. By means of the reaction, the polymers have at least oneaminoaromatic chromophore chemically linked thereto. The aminoaromaticchromophore may be any aromatic compound having a primary or secondaryamino moiety and having a high optical absorbance coefficient. Preferredchromophores have an optical absorbance coefficient of at least about10/μm.

The compositions of the present invention may be dissolved in varioussolvents to provide a composition which is useful for forming thinfilms. The present invention contemplates that the film may be formed byspin casting, extrusion coating, dipping, spraying, or other methodscommonly known in the art. If desired, a photoresist film may be appliedover the antireflective film. Photolithographic processes comprising thestep of applying the antireflective film prior to the patternwise orblanket exposure of the photoresist have improved linewidth controlresulting from a reduction of the standing wave effect and also from areduction of the reflective notching effect.

The present invention also provides methods for the in situ preparationof the novel compositions from precursor compositions comprising maleicanhydride copolymers or glutaric anhydride copolymers or derivativesthereof in combination with aromatic amines. The antireflective film isformed by means of applying the precursor composition to a substrate andheating the substrate to cause further reaction, thus forming a onecomponent antireflective film.

It is an intent of the present invention to provide improved materialsfor antireflective coatings, and a method for the use thereof.

The antireflective films of the present invention have a high opticalabsorbance at the wavelength for which they are intended to be used. Theoptical density is not limited by dye solubility or phase separation.Thus, the film may be thinner than other antireflective films known inthe art. Additionally, some alternative embodiments of the presentinvention have the unexpected advantage of a high refractive index atthe wavelength for which they are intended to be used. This isadvantageous because the required film thickness for an effective BARLis inversely proportional to the refractive index. A BARL which is thinis advantageous in reducing transfer bias, and may also provide improvedfocus and alignment characteristics during patternwise exposure of thephotoresist.

Furthermore, the antireflective films of the present invention provide alow optical absorbance at wavelengths which are longer than thewavelengths for which they are intended to be used. For example, filmsderived from the disclosed compositions which are intended to be usedwith exposing light having a wavelength in the range from about 193 nmto about 300 nm are sufficiently transmissive at wavelengths longer thanabout 320 nm to permit film thickness measurements by interferometrictechniques for process definition and control. Also, films intended foruse with exposing light having a wavelength of about 365 nm aresimilarly transmissive at wavelengths longer than about 425 nm, andfilms intended for use with exposing light having a wavelength in therange from about 365 nm to about 436 nm are similarly transmissive atwavelengths longer than about 460 nm.

Another advantage of the present compositions is that the opticaldensity is not decreased during subsequent processing steps by loss ofthe chromophore. It is known that heating of mixtures of volatile dyesin polymers to temperatures above the glass transition point of thepolymer may cause the dye to sublime from the film. The disclosedcompositions provide a thermally stable antireflective film which is notsubject to decreases in optical density when treated at temperatures ofup to about 250° C. Similarly, the diffusion of the chromophore into thephotoresist layer during any subsequent baking of the resist isminimized or obviated. Furthermore, the chemically bound chromophore ofthe present invention is not extracted by solvent when a photoresistfilm is applied over the antireflective film. The disclosed compositionsare particularly useful in conjunction with photoresist films cast fromsolvents comprising esters such as ethyl cellosolve acetate, ethylethoxy propionate, ethyl lactate, methyl cellosolve acetate, orpropylene glycol acetate.

The antireflective film of the present invention has improved dryetching properties. In CF₄ etching processes, the high selectivity ratiobetween the disclosed BARL materials and the imaged and developedphotoresist causes the BARL material to etch at a faster rate than theremaining resist layer, useful for direct etch transfer processes. Thisallows for another additional variation of a lithographic process inwhich the BARL layer is etched in situ without separate oxygen etchstep, saving time and lowering processing costs. Such uninterrupted CF₄etching of the BARL material and an underlying silicon comprisingmaterial also reduces etch transfer bias. A similar process may be usedto etch through a BARL material overlaying a metal such as aluminum withan uninterrupted chlorine-based metal etch process.

The disclosed compositions are particularly useful in conjunction withalkaline developable photoresist films. The disclosed BARL compositionsresist the action of alkaline developers such as aqueous potassiumhydroxide or tetramethylammonium hydroxide, the developers most commonlyused to develop novolak-diazoquinone photoresists or acid catalyzedpolyhydroxystyrene photoresists. W. Moreau, Semiconductor Lithography,Principles, Practices, and Materials, Plenum, New York, 1988, Chapters 2and 10. This is advantageous because the pattern factor dependenttransfer bias is minimized and a special adhesion promoter is notrequired to prevent lifting.

An additional benefit of the BARL over aluminum layers is that it actsas a barrier against alkaline developer attack on the aluminum layer. Inthe past, this required the use of sodium silicate based developerswhich are harmful to CMOS devices because of the sodium ion present.Higher contrast developers, based on tetramethylammonium hydroxide(TMAH), can be used for the photoresist which allows for even higherresolution.

The antireflective film may be coated with a variety of photoresistmaterials with little or no prior baking of the antireflective layer. ABARL material which permits substrate coating in the same equipment as,and immediately prior to, the application of photoresist without aseparate baking step, saves time and lowers process costs.

Additional uses and advantages of the present invention will becomeapparent to the skilled artisan upon reading the following detaileddescription of the invention and the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention polymer compositions for bottomantireflective layers (BARLs) for deep UV and near UV microlithographyare provided. Deep UV is considered to be ultraviolet light having awavelength in the range from about 193 nm to about 300 nm. Near UV isconsidered to be ultraviolet light having a wavelength in the range fromabout 350 nm to about 436 nm.

The polymer compositions of the invention comprise a reaction product ofa polymer having at least one repeating anhydride group with anaminoaromatic compound having high near UV and/or high deep UVabsorbance. Preferred copolymer compositions have an optical absorbancecoefficient of at least about 10/μm at the wavelength of the exposinglight. More preferred compositions have a high optical absorbancecoefficient over the range of wavelengths of the exposing radiation. Theterm optical absorbance coefficient has been defined by Brunner, supra,and will be a known expression to the worker skilled in the art.

The aminoaromatic chromophore is selected so as to absorb strongly atthe wavelength of the exposing radiation and yet to permit filmthickness measurement on an interferometric tool such as a NANOSPECinstrument and also to permit alignment through the BARL material atlonger wavelengths. For example, films derived from the disclosedcompositions which are intended to be used with exposing light having awavelength in the range from about 193 nm to about 300 nm aresufficiently transmissive at wavelengths longer than about 320 nm topermit film thickness measurements by such interferometric techniques,as previously described.

The aminoaromatic chromophore may be any aromatic compound having aprimary or secondary amino moiety linked thereto, and having an opticalabsorbance coefficient of at least about 10/μm. The aminoaromaticchromophore may be an N-aryl amino compound, a benzyl amine, or anotheraminoaromatic compound wherein the amino group is linked to the aromaticcompound by means of an intermediate group. Preferred aminoaromaticchromophores have a primary amino group. More preferred aminoaromaticchromophores have a primary amino group linked to the aromatic compoundby means of a N-aryl bond. The most preferred aminoaromatic chromophoresare selected from the group consisting of 1-aminoanthracene,2-aminoanthracene, 1-aminonaphthalene, 2-aminonaphthalene,N-(2,4-dinitrophenyl)-1,4-benzenediamine (Disperse Yellow 9, hereafterreferred to as DY-9), p-(2,4-dinitrophenylazo)aniline,p-(4-N,N-dimethylaminophenylazo)aniline,4-amino-2-(9-(6-hydroxy-3-xanthenonyl))-benzoic acid,2,4-dinitrophenylhydrazine, dinitroaniline, aminobenzothiazoline, andaminofluorenone. The worker skilled in the art will appreciate that manyaminoaromatic compounds having high optical absorbance will be useful inthe present invention.

Among the more preferred and most preferred embodiments, many of thedisclosed embodiments comprise aminearomatic chromophores chemicallylinked to polymers by means of an imide moiety, thus forming N-arylimide compounds. It is noted here that in many of the compositionscomprising N-aryl aminoaromatic imides, the π electrons of the aromaticgroup are in conjugation with the carbonyl group of the polymer. Thisextended conjugation results in a red shift of the optical absorbance ofthe resultant reaction product as compared to the starting amine.

While the present invention is described in terms of the N-aryl imidechemical linkage, the skilled artisan will appreciate that many chemicalreactions including the imidization reaction rarely proceed tocompletion and that small quantities of acid, amide, and esterfunctionalities may be exist in the instant compositions. The presenceof such groups in small quantities is anticipated by and is within thespirit of the present invention, provided however, that suchcompositions are essentially insoluble in aqueous alkaline photoresistdevelopers.

The skilled artisan will appreciate that more than one species ofaminoaromatic chromophore may be bonded to the polymeric composition.This may be especially useful for providing a composition havingspecific optical properties at each of several wavelengths of ultraviolet light.

Many of the aminoaromatic chromophores are dyes which are commerciallyavailable from the Aldrich Chemical Company, the Eastman Kodak Company,the Sigma Chemical Company, and like sources. Polymers useful in thepresent invention comprise any polymer having an anhydride group.Particular examples include, without limitation,polydimethylglutarimide, poly(maleic anhydride-co-methylmethacrylate),poly(maleic anhydride-co-vinylmethylether), poly(styrene-co-maleicanhydride), and poly(acrylic anhydride), and derivatives, copolymers,and combinations thereof. Preferred polymers include polymers having a 5membered or 6 membered cyclic anhydride group.

The polymer can have the following repeat units: ##STR1## where R1 andR2 may be independently H, alkyl, phenyl or hydrogen, and ##STR2## whereR3, R4, R5, and R6 may be independently H, alkyl, phenyl or hydrogen.

The polymer can be a copolymer having a first repeat unit having ananhydride group and a second repeat unit having an ethylene group withat least one substituent.

It is known in the art that maleic anhydride monomers which areunsubstituted at the 3 and 4 positions are most amenable to free radicalpolymerizations, however, in an alternate embodiment of the presentinvention, a polymer comprising succinic anhydride repeat unitssubstituted in the 3 or 4 or both positions may be selected for the saidpolymer having an anhydride group.

The present invention contemplates that in another alternate embodiment,a polymer of the general form ##STR3## may be selected for the saidpolymer having an anhydride group, where X, Y, and Z, may beindependently H or any chemically stable functionality, and n is aninteger including 0. Thus the polymer has an anhydride group bondedthrough one carbonyl functionality to the polymeric backbone and hasanother anhydride carbonyl functionality bonded to a pendant group andnot to the polymer backbone except through the anhydride oxygen. Wherethe anhydride group is bonded to the polymer backbone through only onecarbonyl functionality, the aminoaromatic chromophore must be selectedso as to result in a reaction product which is not soluble in aqueousalkaline developers. Thus, it is expected that where the anhydride groupis bonded through only one carbonyl group, the aminoaromatic chromophoremust contain a secondary amine, giving rise to an N,N-disubstitutedamide reaction product.

The present invention contemplates that polymers having a thioanhydridegroup, or other isosteric moieties, may be substituted for the saidpolymer having an anhydride group as a component in similarcompositions.

In the disclosed compositions, the aminoaromatic chromophore ischemically linked to the polymer. The linkage results from any set ofconditions giving rise to a reaction between the amine group of thechromophore and the carbonyl functionality of the anhydride group.Typically the chemical linkage involves the formation of an imide oramide, however, the skilled artisan will appreciate that such linkagemay also involve the formation of other related chemical groups. It isexpressly noted that the linkages of the present compositions arecovalent bonds, and not ionic bonds, charge transfer complexes, norother bond types related to association compounds. In the presentinvention, such covalent chemical bonds are formed by a thermalreaction, however, the skilled artisan will appreciate that othermethods of inducing such reactions exist.

The polymeric compositions of the present invention may be dissolved invarious solvents to provide a composition which is useful for formingthin films. Particular examples of solvents include, without limitation,Γ-butyrolactone, cyclopentanone, cyclohexanone, dimethyl acetamide,dimethyl formamide, dimethyl sulfoxide, N-methylpyrrolidone,tetrahydrofurfural alcohol, or combinations thereof. The preferredsolvents are Γ-butyrolactone, cyclopentanone, and cyclohexanone. In analternative embodiment, traces of a surfactant such as 3M Fluorad FC-430may also be added.

The polymeric compositions of the invention are characterized by beingimmiscible with the photoresist and essentially insoluble in the typicalcasting solvents used in diazoquinone novolak photoresist compositions.The artisan will appreciate that said typical casting solvents used indiazoquinone novolak photoresist compositions include, withoutlimitation: (a) those solvents recited above wherein the instantcompositions are disclosed herein to be particularly useful inconjunction with photoresist films cast from solvents comprising esterssuch as ethyl cellosolve acetate, ethyl ethoxy propionate, ethyllactate, methyl cellosolve acetate, or propylene glycol acetate; each isalso a well known diazoquinone novolak photoresist solvent. The artisanwill further appreciate that said typical casting solvents used indiazoquinone novolak photoresist compositions also include, withoutlimitation: (b) well known casting solvents for diazoquinone novolakphotoresists such as the monooxymonocarboxylic acid esters and ethersthereof disclosed in European Patent Application EP 0-211-667-A to JapanSynthetic Rubber Co., Ltd., and in U.S. Pat. No. 4,943,511 to Lazarus,et al.; and (c), well known casting solvents for diazoquinone novolakphotoresists such as the propylene glycol alkyl ethers and acetatesthereof disclosed in U.S. Pat. No. 4,948,697 to Durham, and; (d) thewell known solvents diglyme and the alkyl cellosolves and acetate estersthereof. Furthermore, it is well known from the teachings of Lin,Multi-Layer Resist Systems, in Introduction to Microlithography,Thompson, Editor, and the artisan will appreciate, that an underlyingfilm forming composition will be immiscible with an overlyingphotoresist composition if the resist casting solvent does not dissolvethe underlying film forming composition, and conversely, an underlyingfilm forming composition will be miscible with an overlying photoresistcomposition if the resist casting solvent dissolves or swells theunderlying film forming composition.

The polymeric compositions of the invention are also characterized bybeing insoluble in the aqueous alkaline developers for suchphotoresists, thus films formed of the compositions are not readilyremoved during wet development. Such films are formed by methods wellknown in the art. The thin films are easily applied and removable by insitu dry etching using the resist image as the etching mask.

It has been found that lithographic patterning on reflective substrateswhich gives rise to an interference effect, and patterning over featureswhich give rise to angular scattering or reflective notching issubstantially improved by the use of the BARL compositions of thepresent invention. The control of line width variations due to standingwave effects over the uneven topography of underlying reflectivefeatures is achieved by the absorbance by the BARL of the imagingwavelengths.

In an alternative embodiment, the composition of the present inventionmay be applied directly to the lithographic substrate without isolation.Thus, the reaction product in solution may be used directly as a castingformulation.

The following examples more particularly describe the preparation andmethod of use of the BARL compositions:

EXAMPLE 1

To a solution of 3.0 grams of maleic anhydride-vinylmethylethercopolymer having a weight average molecular weight of about 50,000 in 75grams of dry pyridine was added 5.4 grams ofN-(2,4-dinitrophenyl)-1,4-benzenediamine (Disperse Yellow 9, hereafterreferred to as DY-9), and the solution was heated to 110° C. for 4hours. When the polymer was fully imidized, as indicated by infrared(IR) spectroscopy, the polymer product was precipitated by pouring thesolution into excess hexane. The polymer product was filtered off, driedin vacuum and dissolved in cyclohexanone to achieve a concentration ofabout 2% by weight, based on the solvent weight. A film having athickness of about 50 nm and having an optical absorbance coefficient ofabout 14/μm was prepared by applying the polymeric solution to alithographic substrate and spinning to achieve a thin, uniform film.

EXAMPLE 2

The polymer product of Example 1 was dried in vacuum and dissolved incyclohexanone to achieve a concentration of about 6% by weight, based onthe solvent weight. A film having a thickness of about 200 nm and havingan optical absorbance coefficient of about 14/μm was prepared byapplying the polymeric solution to a lithographic substrate and spinningto achieve a uniform thin film.

EXAMPLE 3

A solution of 3.0 grams of maleic anhydride-vinylmethylether copolymerand 5.4 grams of DY-9 in 220 grams of cyclopentanone was heated at 130°C. until the imidization reaction was complete. The solution wasfiltered through 0.1 μm filters and applied directly, without isolationof the reaction product, to a lithographic substrate, followed byspinning to form a uniform thin film. The film of 60 nm had an opticalabsorbance coefficient of 14/μm at 365 nm and 22/μm at 248 nm. The filmwas essentially transparent at wavelengths longer than about 450 nm andthe film thickness could be measured by the use of a NANOSPECreflectance film thickness measuring instrument, using a refractiveindex of 1.701 at 6238 Å and the appropriate Cauchy coefficients.

EXAMPLE 4

A solution of 3.0 grams of maleic anhydride-vinylmethylether copolymerand 5.4 grams of DY-9 in 220 grams of cyclohexanone was heated to 130°C. to form the imide product. As in Example 3, the instant compositionwas used directly, without isolation of the reaction product, on alithographic substrate, followed by spinning to form a uniform thin BARLfilm.

EXAMPLE 5

A solution of 2.0 grams of styrene-maleic anhydride copolymer and 5.0grams of DY-9 in 200 grams of cyclohexanone was heated to reflux untilimidization was essentially complete. The imidized product was filteredand was used directly, without isolation of the reaction product, on alithographic substrate, followed by spinning to form a uniform thin BARLfilm. The film had an Optical absorbance coefficient of 14/μm at 365 nm.

EXAMPLE 6

A solution of 3.0 grams of maleic anhydride-vinylmethylether copolymerand 4.1 grams of 2-aminoanthracene in 250 grams of cyclohexanone washeated to form the imide product as previously described. The productwas filtered and was used directly, without isolation of the reactionproduct, on a lithographic substrate. Spinning produced a uniform thinBARL film on the lithographic substrate having a thickness of about 60nm with an optical absorbance coefficient of about 29/μm at a wavelengthof 248 nm.

EXAMPLE 7

The BARL formulation of Example 4 was applied to a 200 mm reflectivepolysilicon wafer by spin coating at 3000 rpm. Subsequently, a 1.2 μmthick film of a diazoquinone-novolak resist was coated over the BARLmaterial and baked at 95° C. for 1 minute. The resist was patternwiseexposed on a 365 nm GCA stepper to form 0.7 μm latent images. The resistwas developed in 0.26N TMAH and the images were transferred by CF₄etching in one step through the BARL material and into the polysilicon.There was no detectable image distortion. No standing waves weredetected by scanning electron microscopy (SEM).

EXAMPLE 8

For a comparison of the effectiveness of various antireflective layersin reducing interference effects, the swing ratios were measured at 365nm by the method of Brunner. The BARL material of Example 3 was coatedon a polysilicon wafer, which was then overcoated with a novolak basedphotoresist. The measured swing ratio of this structure was comparedwith similar structures consisting of photoresist over TiN overpolysilicon, and photoresist alone over polysilicon. The results areshown:

    ______________________________________                                        SWING RATIOS OF A NOVOLAK RESIST OVER POLYSILICON                             USING BARL, TiN, OR NO ANTIREFLECTIVE UNDERLAYER                              Resist/BARL     Resist/TiN                                                                             Resist Only                                          9%              17%      41%                                                  ______________________________________                                    

That the BARL layer was more effective then TiN in reducing interferenceeffects is clearly shown.

EXAMPLE 9

Two sets of silicon wafers were used to show the improvement in linewidth control accorded by use of the disclosed BARL compositions.Reflective polysilicon wafers in a control set were coated with adiazoquinone-novolak resist having discrete film thicknesses rangingfrom 1.00-1.30 μm. The resist was exposed on a GCA stepper, postexposure baked, and developed in 0.26N TMAH. The linewidths weremeasured by SEM. A second set of wafers was first coated with BARLcomposition of Example 4, then coated with the same novolak resisthaving the same film thicknesses as the control wafers. The resist wasexposed, developed, and the linewidths were measured by SEM. Table 1summarizes the relief image linewidths obtained either with or withoutthe underlaying BARL material.

                  TABLE 1                                                         ______________________________________                                        COMPARISON of IMAGES WITH and WITHOUT BARL on SILICON.                        Resist        Resist only                                                                             Resist/BARL                                           Thickness     Linewidth Linewidth                                             ______________________________________                                        1.125 μm   0.72 μm                                                                              0.73 μm                                            1.150 μm   0.79 μm                                                                              0.75 μm                                            1.168 μm   0.87 μm                                                                              0.76 μm                                            1.178 μm   0.97 μm                                                                              0.77 μm                                            1.201 μm   0.94 μm                                                                              0.76 μm                                            1.224 μm   0.86 μm                                                                              0.75 μm                                            1.254 μm   0.79 μm                                                                              0.74 μm                                            Standard Deviations of Line Thicknesses                                                     0.088586  0.013451                                              ______________________________________                                    

It can be seen that linewidth variations are greatly reduced byincluding a BARL composition of the present invention in the processing.

EXAMPLE 10

A polysilicon wafer having 0.5 μm wide lines with sloped side wallsetched into the wafer surface was coated with diazoquinone-novolakresist. Relief images characterized by 0.7 μm long patterns runningparallel and close to the step were produced by exposing at 365 nm anddeveloping the resist. Reflective notching was observed in the patterns.The same pattern was produced in a photoresist layer using an undercoatof the BARL material. No reflective notching was observed in the 0.7 μmpatterns.

EXAMPLE 11

A portion of a solution of 3.0 grams of maleicanhydride-vinylmethylether copolymer and 5.4 grams of DY-9 in 200 gramsof cyclohexanone was filtered, spin coated on a silicon wafer, and bakedon a hot plate at 185° C. for 1.5 minutes. The film was not removed bytreatment with propylene glycol ether acetate, or alternatively bytreatment with 0.26N TMAH photoresist developer solution. As cast, thefilm had a thickness of 61 nm and had an optical absorbance coefficientof 13/μm at 365 nm.

EXAMPLE 12

The reduction in swing amplitude (SA) of photoresist on reflectivesubstrates was evaluated for the BARL formulations of Examples 3 and 6using the model of Brunner, based on the measured refractive index (RI)and optical absorbance coefficient (A/μm) of the BARL at a wavelength(WL) of 248 nm and at 365 nm. The calculated SA was also determined fortheoretical BARLs formulated from the following aminoaromaticchromophores:

BARL-11 Aminoazoaniline

BARL-12 Aminonaphthalene

BARL-13 Aminocoumarin

The swing amplitudes for resist layers either with and without the BARLunderlayer are compared in Table 2.

                  TABLE 2                                                         ______________________________________                                                                SA/BARL                                                                              SA/BARL                                        BARL  WL     SA/NoBARL  calculated                                                                           experimental                                                                          RI   A/μm                           ______________________________________                                         2    365    36%         8%     7%     1.93 14                                 2    248    98%        14%    16%     2.13 19                                 5    248    98%         4%     3%     2.12 31                                11    365    36%         7%            1.89 15                                12    248    98%        11%            2.13 22                                13    365    36%        11%            1.89 11                                ______________________________________                                    

Although the examples are described with respect to compositions usefulat an exposing radiation wavelength of 365 nm, compositions suitable foruse at other wavelengths such as 193 nm, 248 nm, or 436 nm, or withbroadband radiation, may be prepared by selecting the appropriateaminoaromatic chromophores.

Upon a reading of the present disclosure, it will be apparent to theskilled artisan that other embodiments of the present invention beyondthose embodiments specifically described herein may be made or practicedwithout departing from the spirit of the invention. Similarly, changes,combinations and modifications of the presently disclosed embodimentswill also become apparent. The embodiments disclosed and the detailsthereof are intended to teach the practice of the invention and areintended to be illustrative and not limiting. Accordingly, such apparentbut undisclosed embodiments, changes, combinations, and modificationsare considered to be within the spirit and scope of the presentinvention as limited solely by the appended claims.

What is claimed is:
 1. A method for producing an antireflective layer ona lithographic substrate comprising the steps of:dissolving, in anorganic solvent, a composition comprising the imide reaction product ofat least one aminoaromatic chromophore with a polymer comprising ananhydride unit; and applying the solution to a lithographic substrateand removing at least a portion of said organic solvent.
 2. The methodof claim 1 having the additional step of applying a photosensitive filmforming material over said antireflective layer on a lithographicsubstrate.
 3. The method of claim 1 wherein the amount of thechromophore in the composition is greater than the amount of the polymerin the composition.
 4. The method of claim 1 wherein the amount of thechromophore in the composition is greater than about 55 weight percent.5. The method of claim 1 wherein the amount of the chromophore in thecomposition is in a range of about 55 to about 75 weight percent.
 6. Themethod of claim 1 wherein the polymer comprises a repeat unit of theform ##STR4## where R1 and R2 may be independently H, alkyl, phenyl orhydrogen.
 7. The method of claim 1 wherein the polymer comprises repeatunit of the form ##STR5## where R3, R4, R5, and R6 may be independentlyH, alkyl, phenyl or hydrogen.
 8. The method of claim 1 wherein theaminoaromatic chromophore is a primary aryl amine.
 9. The method ofclaim 1 wherein the aminoaromatic chromophore is selected from the groupconsisting of aminoanthracenes, aminonaphthalenes, benzylamines,N-(2,4-dinitrophenyl)-1,4-benzenediamine,p-(2,4-dinitrophenylazo)aniline,p-(4-N,N-dimethylaminophenylazo)aniline,4-amino-2-(9-(6-hydroxy-3-xanthenonyl))-benzoic acid,2,4-dintrophenylhydrazine, dinitroaniline, aminobenzothiazoline, andaminofluorenone.
 10. The method of claim 1 wherein said polymercomprising an anhydride unit is a copolymer comprising a first repeatunit having an anhydride group and a second repeat unit having anethylene group with at least one substituent.
 11. The method of claim 10wherein said first repeat unit is of the form ##STR6## where R1 and R2may be independently H, alkyl, phenyl or hydrogen.
 12. The method ofclaim 10 wherein said first repeat unit is of the form ##STR7## whereR3, R4, R5, and R6 may be independently H, alkyl, phenyl or hydrogen.